doc: add distributor library API change notice

doc: add distributor library API change notice

Given that the packet distributor library improvements (1) will
not be in 17.02, I plan on doing some consolidation of the
API for burst operation for 17.05, merging the two api's into
one, with options for single or burst operation.

(1) http://dpdk.org/dev/patchwork/patch/19911/

Signed-off-by: David Hunt <david.hunt@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>